JPH05243887A - Surface acoustic wave device and manufacture of the device - Google Patents

Abstract

PURPOSE:To improve characteristics by suppressing the bidirectional loss of the surface acoustic wave(SAW) device and reflection loss caused by the discontinuity of an IDT. CONSTITUTION:After forming a metal thin film on a piezoelectric substrate 3, one side face of an electrode finger pattern is inclined or made into a circular arc by executing both of isotropic etching and anisotropic etaching to the same pattern in two times of photolithography processes. The opposite side face is made almost perpendicular to the substrate. Then, SAW 5 are reflected at the terminal part of input/output IDT 1 and 2 because of discontinuity caused by the quantity adding effects of the IDT. Since this reflection coefficient is reduced in the case of smoothly raising the terminal part of the IDT and enlarged in the case of sharply raising it, loss can be considerably reduced by unidirectionally propagating SAW with the asymmetrical cross sectional shape of an electrode finger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device and a manufacturing method thereof, and more particularly to a manufacturing method using a photolithography technique.

[0002]

2. Description of the Related Art In a conventional surface acoustic wave device, as shown in FIG. 4A, an input electrode finger 1 (input IDT: interdigital transducer) and an output electrode finger 2 (output I
DT: Inter Digital Transducer) is patterned on the piezoelectric substrate (3).
At this time, the frequency characteristics are determined by the pitch of the input / output IDTs 1 and 2 and the logarithm thereof, and the energy conversion efficiency at the input / output IDTs 1 and 2 and the bidirectional loss of surface acoustic waves, ID
The reflectance due to T determines the loss between the input and the output.

Further, the manufacturing method of this surface acoustic wave device is as follows.
After a metal thin film was formed on the piezoelectric substrate 3 by sputtering or vacuum evaporation, the IDTs 1 and 2 were formed in a symmetrical pattern in cross section by one-time resist coating, exposure, development and etching operations.

[0004]

In this conventional surface acoustic wave device and the manufacturing method thereof, since the input / output IDTs 1 and 2 are patterned by one exposure, development and etching, each IDT has the structure shown in FIG. As shown in (b), the cross-sectional shape is symmetrical. According to this cross-sectional shape, the AC power applied to the input side IDT 1 is converted into the surface acoustic waves 5 and propagated in both the left and right directions, and since 1/2 of the elastic energy is propagated in the opposite direction to the output side IDT 2, 3 dBm. It will be the above loss. Further, the surface acoustic wave propagated to the output IDT 2 side is also reflected to the input side due to the mechanical discontinuity generated by the mass of the IDT, which increases the loss.

The object of the present invention is to eliminate these drawbacks.
Reduces mechanical discontinuity caused by IDT mass,
A surface acoustic wave device with reduced damage and a method for manufacturing the same.

[0006]

According to the structure of the surface acoustic wave device of the present invention, the cross-sectional shape of each input / output electrode finger, which is a comb-shaped electrode formed on the piezoelectric substrate, in the traveling direction of the surface acoustic wave is
It is characterized in that one side surface is inclined and the other side surface is formed substantially perpendicular to the piezoelectric substrate so as to be bilaterally asymmetric.

The structure of the present invention is a surface acoustic wave device for forming a transducer of a surface acoustic wave and an electric signal by patterning a comb-shaped electrode by photolithography and etching after growing a metal thin film on a piezoelectric substrate. In the manufacturing method of, by using both isotropic etching and anisotropic etching for patterning the metal thin film, one side of the electrode pattern side surface is formed into an inclined shape by side etching, and the other side surface is formed on the piezoelectric substrate. On the other hand, it is characterized in that it is formed in a substantially vertical shape to form an asymmetrical electrode finger shape.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 (a), 1 (b) and 1 (c) show the first embodiment of the present invention.
FIG. 7 is a pattern cross-sectional view illustrating the manufacturing method of the example of FIG. First, as shown in FIG. 1A, Al is formed on the piezoelectric substrate 3.
After forming a thin metal film by sputtering or vacuum vapor deposition, applying photoresist, exposing, and developing, wet etching is performed with phosphoric acid or the like, and both side surfaces of the pattern are formed to be inclined or arcuate. Next, FIG. 1 (b)
After exposure and development are performed using a mask that allows the photoresist 4 to be removed only on one side surface of the Al pattern as shown in, the photoresist 4 is removed by performing isotropic etching such as parallel plate plasma etching. .. Through the above steps, as shown in FIG. 1C, an input IDT1 and an output IDT2 having a side surface inclined on one side and a vertical side surface on the other side are formed.

Next, the operation of the shape of this embodiment will be described. The reflectance of the surface acoustic wave due to the effect of adding mass is large when the piezoelectric substrate 1 is discontinuous, and is small when the discontinuity is small. In this embodiment, the surface acoustic wave 5 generated by the input IDT1 and traveling in the opposite direction to the output IDT2, which is essentially a loss, is reflected by the side surface of its own IDT and travels to the output side. Further, the surface acoustic wave generated in the output direction from the beginning is extremely small in reflection by the input IDT 1 itself and further small in reflection by the output IDT 2, so that the power signal generated at the output IDT 2 also becomes large. Therefore, the loss between the input and the output can be suppressed low as a whole.

The plan view of the electrode finger shown in FIG. 2 shows that the surface acoustic wave 5 generated by the input IDT 1 is unidirectionally transmitted to the output IDT 2.

3 (a), 3 (b) and 3 (c) are sectional views of a pattern portion for explaining the second embodiment of the present invention in the order of steps. After patterning the metal thin film such as Al by anisotropic dry etching as shown in FIG.
After applying the resist 4 as shown in (b) and exposing and developing using a mask so that one side surface of the pattern is exposed,
Wet etching is performed with phosphoric acid or the like to form one side surface of the pattern into an inclined shape to obtain the same pattern as that of the first embodiment as shown in FIG.

[0012]

As described above, according to the present invention, an input / output IDT having a left-right asymmetric cross section is obtained by using both isotropic and anisotropic etching for forming a metal thin film pattern. By realizing this, it is possible to make the surface acoustic wave travel in one direction and significantly reduce the input / output loss.

[Brief description of drawings]

1A, 1B, and 1C are pattern cross-sectional views illustrating a first embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a plan view illustrating the operation of the surface acoustic wave device of FIG.

3A, 3B, and 3C are pattern cross-sectional views for explaining a second embodiment of the present invention.

4A and 4B are a plan view of a pattern of a surface acoustic wave device of a conventional example and a cross-sectional view of a surface pattern portion thereof.

[Explanation of symbols]

 1 Input IDT 2 Output IDT 3 Piezoelectric Substrate 4 Photoresist 5 Surface Acoustic Wave

Claims (2)

[Claims] 1. The cross-sectional shape of each input / output electrode finger, which is a comb-shaped electrode formed on a piezoelectric substrate, in the surface acoustic wave traveling direction is such that one side face is inclined and the other side face is relative to the piezoelectric substrate. A surface acoustic wave device characterized by being formed substantially vertically and asymmetrical to the left and right. 2. A method of manufacturing a surface acoustic wave device, comprising forming a transducer of surface acoustic waves and electric signals by patterning comb-shaped electrodes by photolithography and etching after growing a metal thin film on a piezoelectric substrate. By using both isotropic etching and anisotropic etching for patterning the metal thin film, one side of the electrode pattern side surface is formed into an inclined shape by side etching, and the other side surface is almost perpendicular to the piezoelectric substrate. A method of manufacturing a surface acoustic wave device, characterized in that the electrode finger shape is formed in a left-right asymmetrical shape.